The present disclosure relates to sensor arrays. More particularly, it relates to sensor arrays for sensing and identifying analytes, for example identifying an ambient gas.
Sensor arrays find extensive use in electronic noses for detection of a large variety of volatile compounds. Typically, these sensor arrays consist of a finite number of sensors (e.g., ˜10) with each sensor producing a slightly different response to the analyte (or mixture of analytes). Often the arrays are based on measuring resistance, and materials for the sensor array include, for example, metals, metal oxides, and/or polymers. Metal oxide semiconductors (MOS)-based sensors (n-type: SnO2, ZnO2, TiO2, WO3, etc.; p-type: CuO, TeO2, etc.) may be used to detect volatile compounds (such as acetone, propanol, ethanol) or toxic gases (such as CO, NO, NO2, etc). In general terms, MOS sensors incorporate a sensing layer formed of material selected for a targeted gas. When the targeted gas interfaces with the sensing layer material, the target gas molecules are adsorbed and react on the crystal surface, resulting in a change in conductivity of the sensing layer. By measuring the change in conductivity (e.g., resistivity), the presence and amount (often in ppm or ppb) of the targeted gas (or other compound or analyte of interest) can be estimated. Sensitivity/selectivity to a particular gas depends on the intrinsic properties of the MOS material, and can be modulated by doping to alter the electrical properties or by introducing catalysts such as Au, Pt, Pd to alter the chemical properties. Operating temperature is also a key parameter to optimize sensitivity.
Cross sensitivity to interfering gases is an issue of MOS based sensor devices that remains unresolved. Many strategies have been reported to reduce interferences, including the use of catalysts, and adsorptive or catalytic filters.